CANADA OF CULTIVATED SMUT DISEASES PLANTS DEPARTMENT OF AGRICULTURE OTTAWA - W. J. CHEREWICK CANADA

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3 PUBLICATION 887 AUGUT, 1953 <*. m Agriculture Canadian Agriculture Library m*rm Canada Bibliotheque canadienne de I'agrlculture Ottawa K1 A 0C5 MUT DIEAE OF CULTIVATED PLANT IN CANADA By W. J. CHEEWICK Laboratory of Plant Pathology, Winnipeg DEPATMENT OF AGICULTUE OTTAWA - CANADA

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5 G CONTENT Pace PEFACE 5 INTODUCTION 7 ECONOMIC IMPOTANCE 10 THE FUNGI CAUING MUT DIEAE 13 eedling-infecting mut 13 Flower-infecting mut 14 Local-infecting mut 15 Diemination of mut pore 15 Longevity of mut pore 15 Factor Influencing mut Infection 16 Temperature 1 Moiture 17 oil reaction 17 eproduction of mut Fungi 18 exual reproduction 18 Vegetative reproduction 19 Phyiologic pecialization 19 Hybridization and Genetic 20 Control Method 21 eed treatment 21 eed and eedling examination for the preence of looe mut 25 eitant varietie 25 CLAIFICATION 26 DECIPTION OF MUT DIEAE AND CONTOL METHOD 28 Bunt of Wheat and ye 28 Looe mut of Barley and Wheat 32 Flag mut of Wheat and talk mut of ye 36 Looe mut of Oat and Fale Looe mut of Bailey 38 ( Jovered mut of Oat and of Barley 41 The Looe and the Covered Kernel mut of orghum 43 Head mut of Panicum Millet 44 Millet mut 45 Head mut of Grae 46 tripe mut of Grae 47 ( Jom mut 47 ( )nion mut 50 LITEATUE CITED

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7 PEFACE The lat general account of the mut dieae of cultivated plant in Canada wa prepared by Giiow and Conner in 1929 (mut dieae of cultivated plant, their caue and control). ince then knowledge of the mut fungi, particularly the pecie affecting cereal crop, ha advanced coniderably, making poible a better undertanding of many problem encountered in the control of mut dieae. Invetigation on phyiologic pecialization have led to a new concept of varietal reitance that ha placed the breeding of reitant varietie on a ounder bai. Invetigation on exuality, genetic, and hybridization have thrown new light on the origin of phyiologic race of mut, the inheritance of morphological and phyiological character, frequency of mutation, and pecie relationhip. Improvement in fungicide and treating machine have provided farmer with more effective and eaier method of eed treatment for mut control. Much of thi new knowledge ha appeared in technical paper that are not readily acceible to farmer, teacher, and tudent in Canada. The preent publication i intended to provide them, a well a the general reader, with a brief account of preent-day knowledge of ome of the common mut fungi, the dieae caued by them, and meaure for their control. In a work of uch limited cope, it ha not been poible to do jutice to many intereting and important topic. The ubject matter ha been conidered mainly from the viewpoint of agriculture, but ufficient information about the biology of the mut ha been included to enable the general reader to undertand the procee of development, reproduction, and infection, and the principle underlying control. To tudent of biology, it will be apparent that, notwithtanding the advance that have been made in our knowledge of the mut, many quetion about them till remain unanwered. It i hoped that thi publication may prove of ufficient interet to tudent to encourage ome of them to undertake further reearch on thi intereting and important group of fungi. The author i indebted to Mr. W. Popp for permiion to ue ome of hi unpublihed data; to Mr. W. Clark for taking photograph and preparing plate; and to colleague at the Laboratory of Plant Pathology, Winnipeg, epecially Dr. W. F. Hanna, for helpful uggetion in the preparation of the manucript. W. J. CHEEWICK, Laboratory of Plant Pathology, Winnipeg, Manitoba.

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9 INTODUCTION mut dieae are caued by minute organim, known a fungi (ingular, fungu). The fungi are among the implet form of plant life. The mut, together with the plant rut and muhroom, are member of a large group of fungi known a the Baidiomycete. ince fungi lack chlorophyll, they cannot manufacture their own food and mut depend upon other form of plant life to provide it for them. A great number of fungi live on dead tiue of plant and animal and are known a aprophyte. Many other have developed a paraitic mode of life, requiring living tiue for their perpetuation. The mut fungi belong to the latter group. Thee organim have developed to uch a high tate of paraitim that many any, outwardly perceptible diturbance in the hot tiue pecie caue little, if until formation of their reproductive bodie, known a pore, take place. A a group, mut fungi are paraite, mainly of flowering plant. They develop in the tem, leave, or floral organ and, in ome perennial plant, they invade underground organ, uch a bulb, rhizome, or even root. When in a tate of active growth, the mut fungi conit of delicate vegetative thread, known a hyphae. The hyphae, collectively called mycelium (Fig. 2, A and F), penetrate the tiue of the hot plant and aborb nourihment from them. After a period of development in the hot tiue, the mycelium produce an abundance of pore, technically known a chlamydopore (Fig. 1). In mot of the cereal mut, pore production take place jut before the plant come into head, the pore replacing mot of the normal tiue of the head. In talk mut of rye and onion mut (Fig. 6 and 13), the pore are produced in long treak on the leave, wherea, in corn mut (Fig. 12), they are formed in mae of varying ize, called mut gall, on any of the above-ground part of the plant. The pore appear in practically all cae a a ooty ma. They are comparable to eed of the higher plant inamuch a they reproduce their kind. They are not, however, eed in the true botanical ene. They are minute, roundih cell, each containing a fued or o-called diploid nucleu. mut pore develop from the ordinary cell of mycelium without any pecial pore-bearing organ and, therefore, are called chlamydopore. The mut are mot eaily recognized in the fruiting tage, when pore are produced in variou kind of putule or ori. The oru may be naked or covered (either by tiue of hot origin or a membrane of fungal origin) and it may conit of pore only or contain alo trand of terile mycelium or vacular thread of hot tiue. mut chlamydopore are one-celled and uually occur ingly, but in ome pecie they are united in group, known a mut ball (Fig. 1, C), each compoed of two to everal cell. mut ball uually contain both fertile and terile cell, the latter being colourle or lighter coloured than the fertile cell. The pore are formed from a cloely eptate mycelium, which, generally, i ued up completely, leaving the pore without talk or even car. They uually have a dark-coloured wall either mooth or variouly ornamented. In ome pecie, the pore can germinate a oon a they become ripe, and even when they are till in the oru. In other pecie, they remain dormant for varying period of time. Mature pore in ome pecie of cereal mut may remain viable for everal year. Mot mut can be grown on culture media, and ome pecie form chlamydopore in culture. tudie on exuality, variability, mutation, and other apect of the biology of the mut fungi are often made on culture media, where the entire proce of development can be kept under obervation

10 , rgp> o - o <M b n 0c >^3 ooobq c j bo Oa-" v ',- Figure 1. Photomicrograph of mut chlamydopore. Magnification, 484 app. A Dwarf bunt of wheat (Tilletia carie). B. Ordinary bunt of wheat (T. carie). C. Onion mut (Urocyticepulae). D. Head mut of millet (phacelotheca detruen). E. Covered mut of barley (Utilarjo hordei). F. Burft of wheat {Tilletia foetida). G. Head mut of grae (Utilago bullata). H. Corn mut ( U. maydi).

11 9 About 50 pecie of mut fungi are known to occur in Canada. Many of thee attack plant of little or no economic importance and are of interet only to tudent of the fungi. At leat 17 or 20 pecie (depending on the claification ued) attack cereal, forage crop, and other cultivated plant and may caue coniderable lo if proper control meaure are neglected. Wheat, barley, D t \ rj c r Figure 2. A. Portion of wheat embryo permeated by looe mut mycelium. B. Germinating pore of covered mut of oat {Utilago kolleri), howing fuion between promycelial cell. Fuion of thi type occur commonly in thi and other pecie of Utilago. An infection hypha ha grown out from the promycelium of the lower pore. C. Germinating bunt pore (Tilletia foetida), howing promycelium and terminal poridia. Inet, a pair of poridia joined together by a conjugation tube. D. Germinating pore of covered mut of oat (Utilago kolleri), howing promycelium and poridia a type of germination common to many pecie of Utilago. E. Fuion between compatible poridia of oat mut (U. kolleri). F. Germinating pore of looe mut of barley (U. nuda), howing branching of the promycelium. Magnification, A, 450; B, D, and F, 800; C, 1,300; E, 1,000. (Photomicrograph A, B, D, E, and F by Mr. W. Popp, and C, by Dr. W. F. Hanna)

12 10 oat, rye, corn, orghum, and millet are each uceptible to one or more pecie of mut which have become ditributed throughout the world wherever thee crop are grown. In the abence of proper control meaure, they are reponible for dieae of great economic importance. A i true with mot other micro-organim, the claification of the mut fungi ha been, and till i, in a tate of flux. None of the claification o far propoed i entirely atifactory to all thoe concerned with mut dieae. The mot recent trend ha been to define pecie of mut fungi according to morphological character alone rather than on the bai of paraitim. The author ha followed the grouping of Ficher and Hirchorn (34) and Ainworth and ampon (1), although pecific name a previouly ued in Canada have been retained. ECONOMIC IMPOTANCE mut dieae are almot coextenive with the culture of their hot plant and they contitute one of the mot eriou hazard in the production of many crop. The mut of wheat, barley, oat, corn, orghum, onion, and variou forage grae are well known to Canadian farmer, ince they occur in all part of Canada where thee crop are grown. Etimate of loe caued by different mut dieae have been given by many invetigator (13, 20, 45, 49, 51, 56, 66). Accurate data on the extent of uch loe in any country are difficult to obtain becaue more than one factor i involved. Beide reducing the yield of the affected crop, mut may impair it quality either for eed or for food, and at leat ome mut may be more or le toxic to animal and man. Figure on mut loe are uually baed on reduction in yield and do not take into account other type of injury, ome of which are of coniderable importance. Although mut dieae are till prevalent and detructive, the loe caued by them at preent are inignificant in comparion with the loe experienced before highly effective eed diinfectant were developed. During the early period of agricultural development in Wetern Canada, field of wheat with 40 per cent or more of bunt were not uncommon (45). imilar loe occurred in other cereal crop (51). In the United tate, field of wheat with from 40 per cent to a high a 87 per cent of bunt were often found (66). In uia (101), loe from bunt up to 55 per cent in ome field of wheat were reported in In fact, in ome of the world' bet wheat area, bunt wa the main limiting factor in production. With the development of ucceful eed treatment method, bunt ha practically diappeared from the better-farmed ditrict in Canada, remaining only a an indication of carele farming practice. mut loe in barley and oat in Canada are till heavy. However, with a better undertanding among farmer of the neceity for proper eed treatment of all cereal eed, loe in thee crop could be reduced to a negligible figure. In cereal crop, particularly wheat, two ditinct factor are involved in the loe caued by mut. In the firt place, there i an actual reduction in yield a a reult of the development of mutted intead of normal head, and in the econd, there i a reduction through the weakening of plant that are infected, even though they do not produce mutted head (55, 101). The lo may range from a trace to the greater part of the crop, depending on the percentage of mutted head and infected plant. An additional lo i utained in marketing mutted grain. Dockage, or dicount charged on mutted grain, at elevator amount to a coniderable item if mut i preent in appreciable quantitie. The lower price paid for "mutty" wheat i made neceary by the fact that uch wheat mut be thoroughly wahed before milling, otherwie the flour will be tinted grey by the bunt pore and i likely to have the muty odour characteritic of bunted wheat.

13 11 The approximate lo from mut in field of oat and barley i not difficult to etimate. The percentage of mut may be determined by counting the number of mutted and healthy plant in a given area in everal different place choen at random. From the average percentage of mut thu obtained, the lo in buhel or dollar may be roughly etimated by calculating what the yield of the crop would have been if mut had not been preent. For example, an examination of everal field choen at random in each ditrict of the province of Manitoba in 1948 (13) revealed that there wa an average of 5-8 per cent mut in barley and 1 1 per cent mut in oat. The total production of thee two cereal grain in Manitoba wa approximately 45 and 60 million buhel repectively. The lo reulting from mut would be, therefore, approximately 667,340 buhel of oat and 2,770,700 buhel of barley or, at the average price prevailing during the winter of , a total lo of over $3,500,000. The above figure do not repreent, however, the entire lo caued by mut dieae in thee two cereal. It ha been hown that mut-infected plant are more uceptible to eedling blight and other dieae (55, 128, 135, 157). Alo, infected plant are adverely affected even when they produce no mutted head (101). In experiment at Winnipeg and Lethbridge on phyiologic pecialization in the cereal mut, it ha been frequently oberved that in ome varietie of grain certain race of mut caue an appreciable reduction in the number of eedling and mature plant. Plant of uch varietie may be killed at variou tage of their development. Therefore, the actual reduction in yield would be greater than i hown by the percentage of mutted head or plant, particularly in field where mut i more abundant. Becaue urvey of wheat mut in Canada in recent year have not been extenive, the preent loe from mut in the wheat crop are not well known. Bunt of wheat i probably le prevalent in Manitoba ince the introduction of bunt-reitant varietie of common wheat, uch a egent and edman. In other province, where more uceptible varietie of wheat predominate, no appreciable change in the prevalence of bunt i evident. On the other hand, looe mut of wheat ha probably increaed lightly in Manitoba becaue egent and edman are le reitant than Thatcher, and becaue the durum wheat varietie Carleton and tewart are uceptible to thi dieae. The licening and rapid increae in Canada of Lee wheat, which i highly uceptible to looe mut, may be expected to bring about a further increae in the prevalence of thi dieae. If the prevalence of urface-borne mut pore on eed ample (Table 1) and the number of carload of wheat from Wetern Canada grading mutty (Table 2) are reliable indication of the general prevalence of mut in wheat, then the etimate of the average annual lo in yield becaue of mut, a given by Craigie (20) for Manitoba, would probably be applicable to the whole of Canada. Hi etimate for the year 1916 to 1937 wa f per cent (looe mut J per cent and bunt j per cent). Baed on a total production of wheat in Manitoba for 1948, of 57 million buhel, a lo of f per cent would amount to over 430,000 buhel, or in the neighbourhood of $646,000. A the correponding lo for oat and barley in Manitoba in 1948 ha already been etimated at $3,500,000, it will be een that the combined lo for wheat, oat, and barley in the province that year reulting from reduction in yield by mut wa in exce of four million dollar. The etimated lo in yield caued by mut of the three cereal grain in Manitoba i applicable, in the main, to other province of Canada. A urvey made in 1949 in the three Prairie Province revealed that the prevalence of coare grain mut wa approximately the ame in the parkland area of Manitoba and akatchewan and decreaed only lightly in Alberta. Bunt of wheat, on the other hand, wa much more prevalent in outhwetern Alberta than in the other two province, o the total percentage lo from mut in cereal grain may

14 : car 12 be conidered to be approximately the ame in each of the three province. In Britih Columbia and the eatern province of Canada, mut i known to caue imilar, if not greater, loe in cereal. TABLE 1. OCCUENCE OF UFACE-BONE MUT POE IN AMPLE OF WHEAT, OAT AND BALEY EED FOM MANITOBA, AKATCHEWAN, AND ALBETA 1 Year eed produced ample examined Wheat Oat Barley % bearing ample % bearing ample mut pore examined mut pore examined % bearing mut pore , , , , , , , , , , , , , , , , , , , , x j eult of tet on farmer' eed ample made by the Line Elevator Farm ervice, Winnipeg, Man. Data upplied by Dr. F. J. Greaney, Director. TABLE 2. TOTAL HIPMENT OF WHEAT, AND HIPMENT OF MUTTY WHEAT, FOM POINT IN WETEN CANADA IN THE PEIOD Crop year Hard ed pring Durum Alberta Winter Total car mutty car Total car mutty car Total car mutty car Other Clae Total car mutty car Mean % mutty , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Mean Highet number o gradi ng mutty ince 1915 (3,779 car) incluive Information obtained from the Inpection Branch, Board of Grain Commiioner, Winnipeg, Man From 1915 to 1951 incluive, a period for which record are available, a total of 32,386 carload of wheat from Wetern Canada graded mutty. Thi repreent an average of carload, or approximately 1,313,000 buhel of wheat, grading mutty each year. The dicount on "mutty" wheat varied from year to year and for different grade of wheat, but an average would probably be omewhere between 8 and 10 cent per buhel. In addition, therefore, to the lo in yield already mentioned, a further lo i incurred through the dicount on mutty wheat, which, during the pat 35 year, would amount to approximately $120,000 annually for Wetern Canada. * Loe attributable to impairment of the health and vigour of animal that have conumed grain or fodder contaminated with mut pore are more difficult

15 13 Many controverial tatement are to be found in the literature on to appraie. toxicity or nontoxicity to animal of mut-contaminated feed. Experiment made in Kana (96) proved that corn and orghum mut were in no way dangerou or poionou to hore, cow, and calve. The only diturbance noted wa coughing and neezing at time becaue of the duty nature of the pore. Other invetigator (70) imilarly found that food contaminated with mut pore wa not toxic to any of the ordinary farm animal, although uch food could not be declared harmle under all circumtance. On the other hand, in Montana, according to Giiow and Conner (45), "a lot of cow were fed on mutty hay, and within 12 hour after the firt feed, one-half of them died with ymptom of gatriti and cerebral excitement. No more of the hay wa fed, and no more death reulted. " Experiment in France (23) demontrated that pore of looe mut of wheat were toxic to young mice. Feeding mice on groat mixed with 4 or 8 per cent pore, or injecting them ubcutaneouly with an aqueou pore extract caued hyperaemia accompanied in mot cae by poterior paralyi and, in ome, by intene pruritu. Adult mice were not adverely affected by ingetion of mutted groat. Mayerhofer and Dragiic (91) invetigated corn mut poioning in children at the Zagreb Univerity Children' Hopital and concluded that uch poioning (utilaginim) i cloely allied to true infantile acrodynia, from which it differ mainly in it etiology. Head mut of orghum, phacelotheca reiliana (Kuhn) Clint., may alo be implicated to ome extent in mut poioning in children. On the other hand, according to Zillig (165), Utilago eculenta P. Henn. developing in the inflorecence of Zizania latifolia Turcz., change it to cauliflowerlike gall, which are relihed a a vegetable in China and Japan. In other word, at leat one mut i ued a human food. There i no doubt, however, that ome mut may contain alkaloid more or le toxic to animal, and that mot kind of mut pore, when preent in abundance, make food unwholeome, particularly to very young animal and to pregnant female. THE FUNGI CAUING MUT DIEAE The mut fungi are not confined to cereal and other member of the gra family. They attack a large number of plant pecie belonging to widely different familie. In Canada, mut attack onion, arrow-head, wild tomato, ater, gum weed, and numerou other broad-leaved plant, a well a the cereal and many edge and grae. ome mut attacking perennial plant give rie to ytemic infection and hibernate in the vegetative tate in the overwintering part of the plant. The mycelium pread each year into the growing hoot to produce pore in the appropriate part of the hot. A majority of the mut, however, are annual and, when their pore ripen, the vegetative life of the fungu come to an end. eproduction then depend upon the pore eventually reaching an environment favourable for their development into a new generation. In thi connection, account mut be taken of the production of the mut pore and the time of their diperal, a well a the manner in which they infect their hot. For convenience, the mut under conideration will be grouped into three main clae: eedling-infecting, flower-infecting, and local-infecting. eedling-infecting mut. Bunt of wheat, the oat mut, covered and fale looe mut of barley, and a number of other mut belong to thi group. Thee mut infect their hot plant by mean of pore that are preent on the urface of the eed, or in the oil in cloe contact with the eed. pore of looe mut of oat ometime become lodged under the hull of the eed and, if condition are favourable, they germinate there, producing hyphae that later infect the young eedling. In all intance, the eedling-infecting mut gain entrance to the hot plant by penetrating the coleoptile of the very young eedling.

16 14 When a pore of thi group of mut germinate, it uually produce a clubhaped germ tube, known a a promycelium, on which econdary pore, called poridia, develop (Fig. 2, B and D). The poridia are uually of two oppoite exual group. When two poridia of oppoite ex come in cloe proximity with one another, they become united by a fuion hypha and from it an infection hypha develop. It i the infection hypha that penetrate the eedling coleoptile, thereby enabling the mut mycelium to become etablihed in the underlying tiue of the hot plant. Thu, regardle of how the inoculum i carried, whether on the eed or in the oil, actual infection, under natural condition, take place in the early eedling tage. Once infection i initiated, the fungu advance internally through the tiue of the eedling until, in a uceptible variety, it reache the growing point. From then on it keep pace with the development of the hot plant. When the plant develop to a certain tage of growth, pore formation of the mut fungu i initiated either in the leave and tem, a in the talk mut of rye, or in the head, a in the grain mut of wheat, barley, and oat. The pore mae in mot cae are then blown away by wind or cattered by rain droplet and other agencie and thu contaminate the oil and the eed of healthy plant. The greatet diperion of pore, however, take place during harveting operation. mut pore on the eed may remain viable until the eed i own and begin to prout, when the ame erie of event i repeated. mut pore preent in the oil may be an important ource of infection of fall-own grain, particularly wheat. In northern region, however, the pore do not uually urvive the low temperature of winter and o are of little conequence in the infection of pring-own grain. The eedling-infecting mut may be controlled by ordinary eed treatment with fungicide that diinfect the urface of the eed and to ome extent protect the germinating eed in the oil after planting. The ue of reitant varietie, when available, in conjunction with proper eed treatment greatly facilitate the control of thi group of mut. Flower-infecting mut. The looe mut of wheat and of barley are the only mut of cultivated plant that will be conidered in thi group. The mutted head emerge a little earlier than the healthy head, and pore from them are dieminated during the blooming period of the healthy plant. When a pore alight on a tigma of the hot floret in the proper tage of development, it promptly germinate, forcing it infection hypha through the tyle into the ovary. On reaching the ovary, the fungu produce a mall mat of mycelium in the young embryo (Fig. 2, A) with o little interference to the tiue of the ovary that it develop into an outwardly normal-appearing kernel. When the infection proce i complete, the fungu become dormant and remain o until the eed begin to germinate. Then the mycelium of the fungu become active again and in it growth keep pace with the growing point of the plant until the head i formed. The mycelium uually detroy all the tiue of the inflorecence and, jut before the emergence of the head, replace them by mae of pore encloed in a delicate greyih membrane. The membrane rupture oon after emergence of the head, releaing powdery mae of pore. In a few day the pore are blown or wahed away, leaving a bare rachi intead of a normal wheat or barley head. ince looe mut i carried within the embryo of the eed, it cannot be controlled by ordinary eed diinfectant. Apart from the growing of reitant varietie, the only practical method of control ha been to treat the eed with hot water. Thi method ha not been widely ued, a mot farmer do not poe the equipment needed to control accurately the temperature of the hot water bath. ecently (152) it ha been found that looe mut of barley may be controlled by oaking the eed in a chloranil (pergon) olution. If thi treatment prove to be generally atifactory, it hould facilitate the control of thi mut.

17 15 Local-infecting mut. Corn mut (Fig. 12) i the only repreentative of thi group of mut that i known to occur on cultivated plant in Canada. The chlamydopore overwinter in the oil. During early ummer they germinate producing econdary pore, the poridia, which are picked up by air current and may eventually be blown to young corn plant, cauing local infection. The infection may be on any above-ground part of the plant, for intance, the ear, tael, node, or leaf. After the fungu permeate the plant tiue urrounding the point of infection, a mut gall develop which, at maturity, conit motly of mae of mut pore. The only atifactory way of controlling corn mut i to grow reitant varietie. Crop rotation, detruction of mut gall before they mature, and general cleanline will help to reduce loe from thi mut. Diemination of mut pore In general, the mut fungi are dieminated a chlamydopore which, owing to their minute ize and buoyancy, are readily carried about by air current. Heald and George (59) found that a pore-trap, located a mile and a half from the nearet threhing machine in the tate of Wahington, collected over 10,000 pore per quare inch during one week. Examination of pore-trap expoed at place in Manitoba 1 indicated the preence of mut pore in the air before any of the local crop were in head. The latter obervation prove the longditance diemination of mut pore by wind. Although wind i an important agent in the diemination of mut pore, it i not the only one. Threhing machine, granarie, eed bag, and eedhandling equipment are all important agencie in carrying mut pore from contaminated to clean eed. ain i a contributing factor in the diemination of the mut, inamuch a it wahe down air-borne pore, which may eventually become lodged on the eed of the hot plant. It alo plahe the pore from mutted to healthy head in the field. However, a i true of many other plant dieae, man himelf i the wort offender in dieminating the mut fungi. He tranport mutted eed from ditrict to ditrict, from country to country, and from continent to continent, thu enabling the pathogen of mut dieae to become etablihed wherever their hot plant are cultivated. Longevity of mut pore A few decade ago, before currently known control method were developed, the longevity of mut pore wa a ubject of great practical interet to tudent of mut dieae. The toring of eed grain for a number of year wa conidered a a poible mean of controlling mut until it wa demontrated (160) that chlamydopore, particularly thoe of the eedling-infecting mut, might retain their viability for a long a twelve year. It then became apparent that the germinative power of the eed would be greatly impaired before the infective power of the pore wa lot. mut pore preent in the oil or in plant debri left in the field, and even manure from animal fed on mutted grain, were conidered a probable agent in the diemination of mut dieae. Experiment made at Winnipeg (52) proved that bunt pore, particularly thoe in intact bunt ball in wheat head left on the urface of the oil, may overwinter in Wetern Canada. Neverthele, general experience eem to indicate that in Wetern Canada mut pore overwintering in the field are of little or no conequence in initiating infection in pring-own grain crop. Many of the opre that remain in the field after fall threhing i completed may germinate before the ground freeze. Thoe that fail to germinate in the fall 1 Unpublihed data by B. Peturon, Laboratory of Plant Pathology, Winnipeg

18 16 are ubjected, during the winter and early pring, to drying, wetting, freezing and thawing, and their viability i greatly reduced. The effectivene of eed treatment in controlling mut in cereal grain lend upport to the view that oil-borne mut inoculum i not an important ource of infection in Canada except in winter wheat area, uch a outhern Alberta, where the oil remain relatively dry between threhing time and the eeding of another winter wheat crop, and certain part of Britih Columbia where dwarf bunt of wheat ha been found 1. The relatively high percentage of carload of Alberta ed Winter wheat grading mutty (Table 2) eem to indicate that oil borne inoculum i poibly an important factor in outhern Alberta. The viability of mut pore paing through the digetive ytem of an animal ha been hown (70) to be very low. Only pore paing through pig apparently retained their viability to ome degree, while thoe paing through other farm animal were almot entirely killed. imilarly, pore of corn mut It i lot their viability after having been left in ilage for a few Aveek (107). doubtful, therefore, if mut can be effectively dieminated through 'barnyard manure pread in the field. From a cientific point of view, it i of great interet that mut pore may retain their viability for a rather long period of time. Out of 77 pecie of mut fungi from herbarium pecimen teted by Ficher (32), 24, ranging in age from a few year to a many a 25, contained viable pore. In general, mut pecie of the family Tilletiaceae, to which bunt of wheat belong, howed the greatet longevity. One pecie of bunt contained viable pore after torage in a herbarium for 25 year. Covered mut of barley (Utilago hordei) contained viable pore after 23 year of torage. The pore of the flower-infecting mut ( Utilago tritici and U. nuda) do not retain their viability nearly o long a thoe of other mut. In nature, they are carried by air current to the floret of their hot plant and there germinate and caue infection. ince infection can take place only during the brief period of a week or two while the hot plant are in flower, prolonged viability i of no particular advantage to the pore of flower-infecting mut. However, it ha been found that pore of thee mut, when tored in a cool, dry place, may retain their viability for everal year (144). The mycelium within the embryo of the eed may remain viable for a much longer period (144), probably a long a the eed itelf. Factor Influencing mut Infection mut fungi, like all other plant, are influenced profoundly in their development by environmental condition. Epecially i thi noticeable in the mut carried over from eaon to eaon in the chlamydopore tage. It ha been well etablihed that, at leat among the cereal mut, environmental influence may be operative, not only at the time of infection, but alo throughout the entire growing eaon, and the period of harveting and torage of the eed grain. In other word, mut dieae i a reult of the interaction of hot and pathogen under the conditioning influence of environment. Factor, uch a temperature, moiture, aeration, oil type and compactne, and oil fertility and reaction, play an important part in the development of mut dieae. The influence of ome of thee factor i dicued briefly in the following paragraph. Temperature. The effect of date of eeding on the development of mut wa oberved everal decade ago (19, 150). Elucidation of the factor involved, however, took a relatively long time (14, 28, 30, 31, 61, 72, 85, 93, 101, 115, 116, 139). In general, mut fungi are adapted to the cultural condition bet uited 1 pecimen of dwarf bunt were collected by W.. Foter, Provincial Plant Pathologit, Victoria, B.C.

19 17 to their particular hot. Wheat, for example, i uually own in Canada rather early in the pring, when oil temperature are till relatively low. eeding of oat and barley take place later, when the oil i warmer. The optimum temperature for infection by the bunt organim i C, a compared with C. for the eedling-infecting mut of oat and of barley. Temperature conducive to a very rapid growth of infected eedling after emergence may reult in the plant outgrowing the paraite and producing normal eed (101), wherea temperature or other factor advere to a rapid development of eedling during the pre-emergence period uually increae the incidence of mut (101, 139). With repect to the flower-infecting mut (Utilago tritici and U. nuda), the greatet influence exerted by temperature i during the blooming period of the hot, when infection i taking place. Cool weather prolong the flowering period and, therefore, favour the entrance of pore into the flower, wherea, in a moit warm atmophere and dry oil, flowering proceed rapidly while the head i till in the boot, thu minimizing the chance of flower inoculation (148). Moiture. The fact that the looe mut uually are relatively uncommon in region where the air humidity i low during the flowering period of their hot plant ha long been recognized. Wheat and barley varietie grown under the dry atmopheric condition of California rarely develop looe mut, but, when grown under more humid condition, the ame varietie may prove to be extremely uceptible (136). ain followed by unhine uually caue the head of wheat and barley to emerge before the floret open and later, when the head come into flower, the glume pread widely, thu favouring the chance of flower inoculation. Under humid condition, mut pore on the tigma of the hot germinate and develop infection hyphae much fater than under arid condition. oil moiture doe not eem to have a very pronounced direct effect on the eedling-infecting mut, but, a air i required for the germination of mut pore (83, 160), oil that are poorly aerated, due to an exce of moiture, provide an unfavourable environment for high infection. The oil moiture content required for optimum infection varie with the temperature and other factor but, generally, a moiture content equivalent to per cent of the moiture-holding capacity of the oil i conducive to good infection (14, 28, 30, 31, 61, 71, 85, 93, 115, 116). Apparently mut pore can germinate with le moiture than i required for quick germination of cereal eed (27). elatively dry oil, therefore, like any other factor that may retard the pre-emergence development of hot eedling, i favourable for mut infection. imilarly, in the cae of the local-infecting mut of corn, it ha been oberved that thi dieae i mot prevalent during relatively dry eaon (72). Thi may be partly becaue the inoculum of corn mut i dieminated more readily in dry weather. It ha long been known that eed of oat and barley artificially mutted with the eedling-infecting mut doe not yield conitently a high percentage of mutted plant a naturally inoculated eed. The reaon for thi became obviou when it wa dicovered (37, 141, 163) that naturally inoculated eed contain mut pore and mycelium underneath the eed-hull. The amount of inoculum i thu ubtantially increaed at, or very cloe to, the vital point of attack. A a reult of thi dicovery, the importance of weather condition following pollination and during the maturation period of the crop became obviou. Moiture and temperature condition prevailing during thi period are epecially important in relation to the germination of pore underneath the eed-hull, and thereby influence indirectly the amount of mut in the ucceeding crop. oil reaction. Factor uch a oil type, compactne, and fertility, probably influence mut infection indirectly, by either favouring or hindering a rapid development of the hot eedling and by affecting aeration and other

20 18 oil-environmental factor. oil reaction, however, may have a direct effect upon mut development. Ganer (39) howed that the highet percentage of wheat bunt occurred in andy oil, while in acid moorland and clay oil little or no mut developed. On the other hand, Leukel (83) obtained more mut in clay than in andy oil. Application of lime to acid andy oil increaed mut infection, indicating that acid oil i unfavourable for infection. Other experiment (85, 99) indicate that, at leat for certain mut, neutral or lightly acid oil i the mot favourable for good infection. The above remark on the effect of environmental factor on the development of mut dieae are ufficient to indicate the cloe adaptation of the mut fungi to the condition under which their pecific hot thrive. For a more complete dicuion of the effect of variou environmental factor on the development of the cereal mut, an excellent ummary by Tapke (143) i uggeted. eproduction of mut Fungi It ha already been indicated in the foregoing paragraph that the mut fungi are well adapted to their particular hot in their repone to environmental factor, the diemination and longevity of their pore, and the timing of their fructification. The production of large number of chlamydopore by all pecie of mut fungi enure, not only their urvival, but alo their rapid and widepread diemination. Chlamydopore formation i of further importance in the life cycle of the mut in that it i at that time that exual reproduction take place, and thi provide an opportunity for hybridization and the recombination of variou character, including pathogenicity. The mut fungi do not poe exual organ of any kind, o the exual proce involve merely the aociation and eventual fuion of pair of nuclei. The chlamydopore, or exual form of reproduction, i ditinct from aexual or vegetative reproduction, which i characterized by the poridia. Thee can be grown on culture media in the laboratory very much like the yeat. exual reproduction. In the pecie of mut fungi that have been invetigated, the very young chlamydopore ha been found to contain two nuclei. With the maturation of the pore thee nuclei fue, and it i generally accepted that the mature pore contain a ingle diploid nucleu. A meiotic, or reduction, diviion occur in the germinating pore or in the promycelium and each poridium or hyphal branch ariing from the promycelium receive a ingle haploid nucleu. When compatible poridia or hyphal branche fue, the haploid nuclei preent in them become aociated in pair and from the fued cell binucleate (technically known a dikaryotic) infection hyphae arie. Immediately after infection take place the mut mycelium grow both inter- and intra-cellularly but, a it development progree, more and more mycelium become intercellular, deriving it nourihment from the hot cell by hort hyphal branche (1). Jut before fructification the mycelium branche profuely, producing variouly curved, curled, or branched hyphae which force the hot cell apart and form a mut oru. The individual cell of the mycelial mat in the oru eventually eparate, develop thicker wall, and turn into pore. In ome pecie, practically all the hyphal cell in the oru develop into chlamydopore, wherea, in other, ome cell loe their dikaryophae and become either terile acceory cell, a in the pore-ball of Urocyti pp., or form a membrane around the oru, a in phacelotheca pp. Unlike the cereal rut, which can continue indefinitely their vegetative reproduction (in the 4 uredial tage), the mut fungi reproduce exually in every chlamydopore generation. A phyiologic race of rut remain unchanged through ucceive generation of the uredial tage, unle a mutation occur, even though it i not in a homozygou or true-breeding condition. On the

21 19 other hand, a phyiologic race of mut, unle it i homozygou, may be expected to undergo egregation during the exual proce that accompanie the formation of chlamydopore in each generation, and o give rie to new race. From the viewpoint, of pathogenicity, therefore, an important ditinction mut be made between race of thee two group of fungi, the rut and the mut. Neverthele, by continuou election and purification a phyiologic race of mut can be reduced to a pure-breeding condition with repect to pathogenicity. Vegetative reproduction. On artificial media, the mut fungi may be cultured a monoporidial, or haploid, line that will continue to reproduce without genetic change except through mutation. Monoporidial culture are regularly employed in tudie on the genetic and hybridization of the mut fungi and ometime in the iolation of phyiologic race. ince monoporidial line reproduce readily on artificial media it i poible that they reproduce alo in nature. poridia of corn mut, for intance, have been oberved to germinate and multiply in oil and in moiture that collect in leaf axil (75, 110). The bet known example, however, of the vegetative reproduction of mut fungi in nature i provided by onion mut, Urocyti cepulae. Anderon (3) found that pore of thi organim may germinate in the oil and develop a coniderable amount of mycelium that can, under favourable condition, maintain it viability for many year. Thi mycelium may break into mall piece that perit in a dormant tate for ome time, and then tart to grow again when favourable condition return. Vegetative reproduction may continue in thi manner for a number of year in the abence of the hot. Phyiologic pecialization According to eed (112), phyiologic pecialization in plant pathogenic fungi wa conidered a early a 1879, but it wa not until 1894, when Erikon, a ditinguihed rut invetigator, publihed the reult of hi experiment, that the exitence of thi phenomenon wa etablihed beyond doubt. Hi dicovery marked one of the mot important advance in the tudy of plant dieae fungi. Kniep (76), in 1919, wa the firt to ugget the occurrence of phyiologic race in the mut fungi. He noticed difference in the appearance of poridial culture of the anther mut of violet (Utilago violacea Per.). Not long afterward, it wa demontrated (164) that phyiologic race of thi mut could be differentiated on the bai of their ability to infect certain member of the Caryophyllaceae and not other. In other word, collection of the ame mut fungu, although appearing alike morphologically, differed in their paraitic behavior. In hi tudie on the effect of environmental factor on the infection of barley varietie by covered mut (Utilago hordei), Fari (28) ubjected, in the greenhoue and in the field, a group of varietie to three different collection of the mut and found ditinct difference in their pathogenicity. Furthermore, when Hannchen barley wa inoculated with pore from mutted head of that variety, 72 per cent infection wa obtained, but, when Hannchen wa inoculated with pore from hooded barley, collected in the ame ditrict, infection wa only one per cent. Fari concluded that difference in the pathogenicity of different collection of mut could be explained only on the bai of "pecialized race" of the fungu. In hi pioneer work on phyiologic pecialization in the cereal mut, he iolated five race of U. hordei. eed (113) tudied two collection each of the looe and covered mut of oat (Utilago avenae and U. kolleri) and found two ditinct race in each of them. The claical invetigation of Fari (28, 29) and eed (113) were oon followed by imilar tudie on other mut of agricultural crop (17, 22, 67, 98, 106, 121, 145, 162) and phyiologic race were found in all the pecie' tudied. The number of known race in each of the mot important mut fungi i increaing

22 rapidly. 20 For example, in the United tate, there have been decribed 31 race of the mooth and the rough-pored bunt fungi (Tilletia foetida and T. carie) (120), 22 race of the looe and covered mut of oat (Utilago avenae and U. kolleri) (69), 11 race of looe mut of wheat (U. tritici) in the eatern oft wheat region (8) and 11 race in the hard red pring wheat region (100), 13 race of covered mut of barley (U. hordei) (142), and 13 race of fale looe mut of barley (U. nigra) (145). In Canada, tudie on phyiologic pecialization in the cereal mut at the Laboratorie of Plant Pathology, Winnipeg and Lethbridge (12), indicate the preence of at leat 13 race of covered mut of barley (Utilago hordei), 12 race of fale looe mut of barley (U. nigra), 10 race each of the looe mut of wheat and barley (U. tritici and U. nuda), 5 race of covered mut of oat (U. kolleri), 14 race of looe mut of oat (U. avenae), and 15 race of mooth and roughpored bunt of wheat (T. foetida and T. carie). Other invetigation on phyiologic pecialization in the mut fungi have been reported in different countrie and the total number of race identified i, no doubt, much higher than that found for the United tate and Canada. However, ince different invetigator have not ued the ame varietie of hot crop to differentiate race, a comparion of their reult i not yet poible. Hybridization and Genetic In attempting to produce mut-reitant varietie of agricultural crop, the plant breeder i at once confronted with the quetion of the tability of the paraite. The fact that the mut fungi are compoed of numerou phyiologic race in itelf greatly complicate the breeding problem. The tability of thee race, their origin, and the poibility of new one ariing that may be able to attack varietie reitant to exiting race, are all matter of great interet and importance. The increaing amount of mut in previouly reitant varietie (62), emphaize the neceity of obtaining fundamental information concerning, not only the prevalence and ditribution of phyiologic race, but alo the poibility of new race ariing by hybridization both within and between pecie of mut fungi. Although fuion of poridia in certain mut had been oberved by earlier invetigator, Kniep (76), in 1919, wa the firt to how that fuion occur only between certain pair of poridia. Thi dicovery led him to conclude that the mut with which he wa experimenting (Utilago violacea) mut conit of two exual train or, in other word, that it wa heterothallic. Zillig (164) confirmed the work of Kniep and alo howed that conjugation occurred between exually oppoite train of different phyiologic race. In hi further work, Kniep (77) oberved conjugation between poridia of a number of mooth-pored pecie of Utilago, between ome echinulate-pored pecie, and alo between ome of the reticulate-pored pecie. He obtained conjugation between certain moothpored and echinulate-pored pecie, but no conjugation were oberved between poridia of reticulate-pored pecie and thoe of either mooth- or echinulatepored pecie. Dickinon (24) oberved hyphal fuion on the hot tiue between monoporidial culture of U. hordei and U. nuda, but he did not grow hi plant to maturity to determine the outcome of uch fuion. Thee invetigation proved beyond doubt that interpecific fuion are common in the mut fungi, but none of them howed that interpecific croe were able to caue infection of the hot plant. Hanna and Popp (50) found that Utilago avenae and U. kolleri are heterothallic and that the poridia of each pecie conit of two ex group. Monoporidial culture mated readily with thoe of oppoite ex of the ame or the other pecie, and plant inoculated with interpecific hybrid produced mutted

23 21 panicle intermediate in appearance between the looe and covered type. The hybrid chlamydopore were echinulate. In later invetigation (109), proof of dominance of the factor for echinulate pore over that for mooth pore wa obtained by back-croing the Fi hybrid with both of the parent culture. In hi tudie on hybridization between Tilletia pecie, Flor (35) obtained infection of wheat plant by hybrid of T. carie and T. foetida. imilar tudie have be^n made of phacelotheca orghi and. reiliana (151), and of Utilago hordei and U. nigra (2), and in each cae the hot plant became infected with the mut hybrid. Croe between U. hordei or U. nigra and U. avenae, U. kollerij and U. tritici led to hyphal fuion and the initiation of infection hyphae but plant infection failed (2). The invetigation ummarized in the foregoing paragraph how clearly that new race of the mut fungi may originate through hybridization, both between exiting race of a ingle pecie and between cloely related pecie. Field obervation indicate that new race appear frequently in nature, and it i probable that many of them are of hybrid origin. It i well known, for intance, that when varietie of wheat having reitance to the prevailing race of bunt are grown, new race virulent to them tend to appear (64). imilarly, the occurrence in the field of mutted oat panicle, intermediate in appearance between the typical looe and covered mut (109) may be attributed to interpecific hybridization. On the other hand, there i evidence (2, 158) that, under natural condition, certain of the poridia-forming mut fungi initiate the binucleate or paraitic phae through fuion of adjacent promycelial cell (Fig. 2, B). uch a proce would tend to reduce the opportunitie for new race to arie through hybridization. A further complication with repect to hybridization and phyiologic pecialization in the mut fungi aroe when it wa dicovered that there may be more than two mating group in ome pecie. Hanna (46), tudying the corn and orghum mut Utilago maydi and phacelotheca reiliana, found that in each of thee pecie ome chlamydopore produced poridia belonging to four mating group. Flor (35) concluded that there are four or more uch group in Tillitia pp., but later Holton (65), tudying a large number of monoporidial culture of Tilletia pp., wa able to find only two mating group. The total number of factor governing the mating of haploid culture ha not a yet been determined with certainty for any mut pecie. A a wider range of material i tudied, additional factor are likely to be found. For the preent, however, it may be concluded that by far the mot common condition in any one pecie i two mating group. For a more complete ummary of literature on the cytology and genetic of mut fungi "The Britih mut Fungi" by Ainworth and ampon (1) i recommended. Control Method mut dieae may be controlled by eed treatment, the growing of reitant varietie and, in ome intance, by crop rotation. In general, good farm practice contribute to mut control. eed grain hould be of high quality and well cleaned, a cleaning remove mut ball, debri, and coniderable number of mut pore. With the aid of eed treatment, it i relatively eay to control mut in partially reitant varietie, but uceptible varietie require careful and regular treatment to keep down mut loe. eed treatment. eed treatment for the control of mut, particularly bunt, ha been practied for the lat three centurie. Before the true nature of mut dieae wa known many farmer conceived variou method of treatment on the theory that certain timulant were needed to enable the eed and